Decolorizing and improving metal salts of partial esters of dithiophosphoric acids



DEcoLomz'nsro AND IMPROVING METAL SALTS F PARTIAL ESTERS 0F DITHIOPHOSPHORIC sg. Joseph 'Boha, -Fort Lee, and Charles H. Kolker, Maplewood, NJ., assignors to Gulf Oil Corporation, Pittsgburgh, Pa., a eorpora tion of Pennsylvania v No Drawing. Filed Mar. 11, 1959, Ser.No; 798,612

. .1] clai mm-429.9

Thisfinvention'relates' toidecoloiizing and improving metal 'salts ofpartial esters of dithiophosphoric acid.

- Oil soluble salts, especially po;lyvalent metal salts of 0,0 "-diest ersf of ldithiophosphorie acid, have found extenare" use; ra ydrocar on lubricating oils because of their .1 f ,an'ticor'ros'ion and antiwear properties. A's isw ell known, these oil-soluble metal salts are conventionally prepared 'by' reacting mon'ohydric' alcohols or phenols with"phosphoruspentasulfide, usually in the mol proportion of 4:1, at temperatures in the range of 130 to. 350 'F. tofo'rmpartial esters of dithiophosphoric acid, and then by reacting th e'thus-obtained partial esters with a basic metal compound at temperatures in the range of 60 to 280 'F., toform thecorresponding metalsalts of thepartial esters of dithiophosphoric acid;

It has been found that very often the'oil solublemetal salts prepared as described above 'will be objectionably dark in'color, usuallygreenish, even whenthe reaction conditions are controlledcarefully'. The dark color-"is objectionable as I afi'ects the 'mauketability of the'salts. Also the 'oil soluble metal salts referred tdabove ire 7 Patented May 9, .1961

. phenol and the like? The presentinvention includes the 1 process described as well as the product thereof.

Although the causeof the dark color in metal salts of dithiophosphate'esters has not been definitely established, it is believed that such color arisesfrom the presence of traces of heavy metals, principally iron, in the phosphorus pentas'ulfides, commercial grades of which frequently contain about 15 to 60 parts perrnillion heavy metals calculated as sulfides. "Nor has the mechanism by which decolorization takes place been conclusively determined. It is'considered that the trialkylolamine forms complexes with the traces of heavy metal compounds in the dithiophosphate ester salt that'are more stable than the uncomplexed metal compounds. negatived by the fact that other agents capable of forming complexes with heavy metal compounds do not produceequivalent'results The .trialkylolamine employed in this invention need not be pure. For example, commercial mixtures containing monoand di-alkylolamines can be used. However,

, the'trialkylolamine employed in the present invention should contain less than about 50 percent of monoand di-alkylolamines,- as these materials are appreciably less effective than trialkylolamines for the purposes of this invention, and therefore necessitate the use of relatively larger propo'rtions of the decolorizing agent. The use of larger proportions of the'decolorizing agent is undesirable as such use imparts an objectionably largenitrogen content to the dithiophosphate.

Any amount of trialkylolamines that will improve the color of the dithiophosphate salts without adversely af fect-ing other properties'of the salts-can be used. Any

quently exhibita rather low pH,'often less than'5, despite I fuse ofequivalent orgreater proportions of basic metal compound 'fdurin'g "salt formation. A low pH is' objectionable in rnetai salts of partial-esters-ot dithiophosphoric acids,"as it afiects 'theycompatibility"of the salts in lubricants with ot' alkalinepH.-* r I It has .now vbeen found that the metalsalt's of partial estersoi' dithiophosphoric acids can be substantially dec olorize'd and made less acidic *by' incorporation therein of -,sman*amounr of a nialkylolamine whose 'alk ylol groups contaiiif l totcarbonatoms each, whereby-such salts are rendered moresuitable' for' useas improvement agents in hydrocarbon oil lubricants." Excellent 'results have been obtained with triethanolamine, but other trialkylolamines ofthe class disclosed can' be'used. Excellentresults are obtained with 0.2 'to' 0.75 percent by weight, ot,-the irialkylolamine,but larger or smaller amounts canbe use or example; there can belused 0.05 to 1.0 percent by w eight. "The iii'ventionhas' been found especially advantagwus in connection with zinc and calcium salts of diesters of dithiophosphoric acid such as the 0,0'-diocty-l esters, but it can be used in con nection with other metal salts of other partial diesters of dithiophosphoric acid. For example, the invention can be used with alkali metal salts such as sodium and potassium salts, alkaline earth metal salts such as barium and strontium salts, other Group II (Mendelyeevs Periodic Table) metal salts such as magnesium salts, of partial esters of dithiophosphoric acid, such as di(2-ethylhexyl) dithiophosphoric acid, O,Q-di(cyclohexyl)dithiophosphoric acid, 0,0-.di(methylcyclohexyl)dithiophosphoric acid. Examples of other partial esters are the 0,0'-dialky-l dithiophosphate esters ofprimary monohydric alco- 1 hols containing 3- to 20 carbon atoms per molecule, and

- the corresponding esters of-phenols such as phenol: and v alkylated phenols such as cresol, octylphenol, nonylerimprovement'agents that have an insure thorough admixture of the materials, but this is amount of the trialkylolamines that will producea suit able improvement in color will also produce a useful improvement in pH. i An appreciable improvement in color can be obtained by theuse'of as littleas 0.05 percent trialk-ylolamine by Weight of the metal salt. A major improvement is normally obtained by the use of proportions in therange of about 0.2 to 0.75 percent. However, larger proportions can be 'used. -For example, good results' can be obtained with up tozabout 1.0 percent trialkylola'mine. Proportions substantially greater than 1.0

percent are undesirable as such proportions undulyincrease {theunitrogen content of the 'dithiophosphate salts. 1 The trialkylolamine isadded to the dithiophosphate I salts-:after;thesalt-forming reactionbetween the metalcontainingbaseand the dithiophosphoric acid ester is complete; This is done inorder to avoid preferential reaction of the trialkylolamine with the dithiophosphoric acid, ester ,rather than color-forming components, and in order-that the metal content (derived from said base) of the sa lt will not be diminished. l v v ,7 The J decolor'izing' reaction ,takes jplace spontaneously at. am" nt atmosphericternperatures"and no further treatment is"necessary; The trialkylolamine' can be added "in any convenient manner. Some agitation is desirable to not essential. v

The etiectiveness of the present invention was demonstrated upon a sample of a green plant-scale batch of calcium-zinc 0,0'-di(Oxo octyl) dithiophosphate having acolor greater than 1.5 ASTM union scale. sample there was added 0.5 percent by weight triethanolamine. The green color disappeared, and the color was lightened to less than 1.0 ASTM union.

In a specific embodiment of the invention 0,0'-dioctyldithiophosphoric acid isprepared by adding 222 pounds (1 pound mol) phosphoruspentasulfide, containing .15 to 60' p.p.m.heavy metals, over a period of about four hours to about 533- pounds (approximately 4 pounds mole) of Oxo-octyl alcohol .(mixedfbranched-chain octanols; mostlydimethylhexanols prepared by thegQxo However, this is somewhat synthesis process)" over a temperature range of 50 to 95 C., the temperature at the end of the reaction being about 90 to 95 C. The mixture is agitated several hours after addition of the phosphorus .pentasulfide to complete the reaction. The resulting0,0'-dioctyldithio-" phosphoric acid is then converted to salt-form Salt formation is effected by adding 1425 pounds (17.5 pound mols) zinc oxide to 11,900 pounds (33.6 pound mols) or of the zinc oxide and during the onehour holding period thereafter, nitrogen is bled into the reaction, mass at a rate of 1000 to .1100 cu'. per hour.,; The reaction mass is then treated with about 150 pounds of methanolic hydrated lime, The batch of calcium-zinc O ,O'- dioctyldithiophosphate is then filtered through a .precoated filter press. To the greenish product there is then added about 50 pounds (approximately*0.5 percent by weight) of a commercially-obtained triethanolamine. The color of the resulting product is lighter than 1.0 ASTM union, and the pH is greater than 5. p I

It will be understood that the invention is not limited to themetal salts or deeolorizing agents of the foregoing embodiment and that other salts and other decolori zing agents "referred to herein can be substituted for those in the foregoing embodiment in equivalent proportions in the invention is limited only by the scope of the claims appended hereto.

We claim: 1. A process comprising incorporating a small amount, sufiicient to reduce the color of the product, of a trialkylolamine whose alkylol groups each contain 1 to.4 carbon atoms, in a metalsalt of a partial ester of. dithiophos-Y phoric acid that contains an objectionable amount of color-forming components, said small amount 'being not greater than about 1.0 percent by weight of said salt.

2. The process of claim 1 where the. trialkylolamine about 0.05 to 1.0 percent by weight of said salt.

4. The process of claim 1 where said small amount is about 0.2 to 0.75 percent by-weight of said salt.

5. The process of claim 1 where said metal is at least one member selected from the group consisting. of zinc and caleiumjand said partial ester is OO'-dioctyldithiophosphoricacid. p Q6. A process ,comprisingfreact'ing a'member's'elected from "the group consisting of monohydric am ne-1s? and monohydric phenols with phosphorus pentasulfide? that has an objectionable heavy metals contentin the mol proportion .o f.about 4:1, at atem'perature in the range of about 130 10 350 F., to form a partial ester of di-f thiophosphoric acid, reacting said partialester with a basic: compound of a metal selected from the groups conan obvious manner. For example, there can be used triisopropanolamine, tripropanolamine, and tri(2-ethyl, 12- hydroxyethyDamine. Trimethanolamine can also be used where; the consequentreduction in flashpoint is not objectionable.

As has been mentioned, the use of trialkylolarnines in accordance with the present invention improves the color of the metal salts of dithiophosphoricacid esters and im proves their compatibility in hydrocarbon oils with other addition agents. In addition, available experimental evi dence shows that lubricating oils containing thiophosphate salts prepared. in accordance with thisinventiondo not produce increased engine deposits during engine. operation as compared with oils containingconventional thiophosphate salts, andin fact, the former can tend vtorreduce.such;deposits. In addition, the advantages named are obtainedwithout formation of undesirable c olors, haze or the like, and without increasing the foaming tendencies or water sens itivity, and without unduly increasing the nitrogen content of the salts.

It willbe understood that many variations and modifif out departing the spirit of theinvention, flandthat sisting of alkali metals, alkaline earth metals, Zinc and magnesium, at a temperature in. the range of about60" to 280 F. to form the corresponding metal salt ofsaid partial esterfand incorporating insaid salt a small amount, sufficient to reduce the color of theproduct, of a trialkylolamine whose alkylol groups each. contain 1 to,4 carbon atoms, said small amount being not greater than about lfi percent by weight of vs aidsalt Y f .7. ,A composition comprising a major proportion of a metal salt ofa partial ester of dithiophosphoric acid that contains an objectionable proportion of color-forming components, and having combined .therewithiia small amount, suflicient to reduce the color of the-salt, of a trialkylolamine whose alkylol groups each containl to 4 carbon atoms, said small amount being not greater than about 1.0 percent by weight of said salt;

8. The composition of claim"7 where said trial kylolaminetisltriethanolamine. H t t H p 9. 'I'he:eomposition of claim 7 where saidsmall amount is';about.0,2 ,to 0.75 percent'by weight otth e salt. 1 $10.. The composition of claim .7 where said metal is at leastione member selected from the group consisting of zincx-and calcium, andsaid partial .cster is;Q,Q' dioctyl dithiophosphoric acid. it

References Cited in the fileoif this patent UNITED STATES PATENT OFFICE CERTIFICATE OFCGRRETION Patent No 2,983, 742 May 9, 1961 Joseph Boloa et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 7, for "17- 5" read 1706 a,

Signed and sealed this 26th day of September 1961., v

( SEA L) Attest:

ERNEST W. SW'IDER DAVID L. LADD f Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF GORREUIMN Patent No 2,983, 742 May 9, 1961 corrected below.

Column 5 line 7, for "1705'" read 1706 0 Signed and sealed this 26th day of September 1961.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer I Commissioner of Patents USCOMM-DC 

7. A COMPOSITION COMPRISING A MAJOR PROPORTION OF A METAL SALT OF A PARTIAL ESTER OF DITHIOPHOSPHORIC ACID THAT CONTAINS AN OBJECTIONABLE PROPORTION OF COLOR-FORMING COMPONENTS, AND HAVING COMBINED THEREWITH A SMALL AMOUNT, SUFFICIENT TO REDUCE THE COLOR OF THE SALT, OF A TRIALKYLOLAMINE WHOSE ALKYLOL GROUPS EACH CONTAIN 1 TO 4 CARBON ATOMS, SAID SMALL AMOUNT BEING NOT GREATER THAN ABOUT 1.0 PERCENT BY WEIGHT OF SAID SALT. 